I wish I had a solution for you. All-butter American style buttercreams will crust a little bit. I think you should just treat yourself and make a cake just for you with a non-crusting icing. You deserve it after a c-section! Better yet, have someone make it for you!!!

You could try a 7 minute frosting...egg whites, granulated sugar, no fat... it is not a crusting buttercream, but it tastes good if eaten the same day it is made... You can also freeze it, with fairly good success. It makes nice borders etc. (See santa cake in my photos).

Any frosting that has more sugar than fat should crust slightly after a while.

I would definitely explore that vitamin K thing with your ob/gyn or regular doctor. They have just released a study that says that calcium is best absorbed the right way coupled with vitamin K. If you are on blood thinners for the rest of your life, you could have other problems down the road.

Also do all shortening have too much vitamin K or is it the type of vegetable oil that is the base. Crisco is used with soybean oil, which I detest. Spectrum is made with palm oil. I do not know the vitamin levels in this two ingredients, I'm just throwing it out there that not shortenings are made alike, so not all shortenings may have loads of vitamin K.

Theres the old fashioned cooked frosting, but I don't remember if its a crusting frosting. I haven't made it in years and back then I didn't bother with smoothing icing, I just spread it on my cakes any old way.

Theres a slew of cooked frosting recipes on google. Look for Red velvet cake with cooked frosting and you'll find lots of variations.

I'm adding this link for you too. Its a food data list that you can search to find out how much vitamin K is in different foods. Easy to do, just put in the food item and it'll give you a rundown of how much vitamin K is in different amounts of the food.

The buttercream frosting I make is an all-butter buttercream and I've never had any problems with getting it to crust. the recipe I use is basically 2 sticks of butter, a 2 lb bag of powdered sugar, about 2 tsp vanilla extract, and a little milk (enough to get the right consistency). I can't stand shortening-based frostings. They always seem to leave a greasy slimy feeling in my mouth.

Italian or Swiss Meringue buttercreams do not crust, but are a dream to smooth on and taste SO much better than shortening based buttercreams. I haven't used a shortening based buttercream since the Wilton class many years ago and I live in South Florida.